Not applicable
There is an increasing need to extract beneficial effect (e.g., power and/or refrigeration) from low temperature heat, which is frequently regarded as waste heat. Heat-activated absorption cycles provide exceptional promise in this regard.
Many low temperature heat sources have a temperature glidexe2x80x94the more heat that is extracted, the lower the temperature becomes. All sensible heat sources have that characteristic, e.g., exhaust combustion gas from an engine or furnace, hot process liquids, or geothermal liquid. Pure component latent heat (e.g., saturated steam) is isothermal, but mixed component condensation has a glide. Solar radiation may be regarded as isothermal, but once it is captured in a heat transfer fluid it has a glide.
In order to extract maximum useful effect from a glide heat source, the application process needs to accomplish two equally important objectives: the heat acceptance should have a glide comparable to that of the source, and it should reduce the source temperature a maximal amount. These two considerations respectively denote the quality and the quantity of heat input.
In principle absorption cycles excel at those two objectives, since they are thermodynamically capable of accepting heat input with temperature glide, and also of being powered by heat down to very low temperatures, e.g., less than 100xc2x0 C.
However, the prior art practice in heat-activated absorption cycles does not make full use of this capability. Flame powering or steam powering has no need for itxe2x80x94all the heat is input at the hottest end of the hottest component of the cyclexe2x80x94the generator. In volatile absorbent cycles, that component is also known as the reboiler.
Prior art examples of inputting heat to absorption cycles are found in U.S. Pat. Nos. 3,690,121; 4,307,572; 6,357,255; and International Publication WO 01/94757.
With a volatile absorbent, the process of desorbing the sorbate vapor from the sorbent liquid is effectively distillation. When heat is referred to as xe2x80x9clow temperature,xe2x80x9d it signifies that at least part of it is at a temperature below the peak distillation or de sorption temperature.
In its broadest aspect, this invention discloses the distillation of a fluid mixture using low temperature glide heat. Distillation is generically useful in many applications, and this disclosure allows it to be accomplished with lower temperature heat than heretofore possible. The particular focus of this disclosure is on distillation incorporated in an absorption cycle with a volatile absorbent, and with useful effect either chilling or power.
Thus included among the objects of this invention is to achieve more beneficial distillation effect from a given low temperature glide heat source than has heretofore been possible, and in the context of an absorption cycle, to achieve more refrigeration and/or power from that source than heretofore possible.
The above and additional useful objects are obtained by an apparatus for distilling a fluid mixture using low temperature heat comprised of:
a) a distillation column;
b) a heat recovery vapor generator (HRVG);
c) a splitter for the fluid mixture, which directs a minor fraction to the upper reflux portion of the distillation column, and the remainder to the heat recovery vapor generator;
d) a flowpath for two-phase fluid from the HRVG to the lower portion of the distillation column; and
e) a heat exchanger in the central portion of said column which is supplied column bottom liquid.
Related variants of this disclosure extend to various sensible heat recuperation schemes between column fluids, and to the use of more than one heat recovery vapor generator in series, as described further below.